All programs are written in one or the other programming language. The lines of text that comprise the program is known as the source code. The source code (or source as it is usually called) can run into tens of lines or into millions of lines. It contains variable declarations, functions, loops, instructions, and other statements that define the functioning of the program. Programmers often add “comments” to their source to ensure that they and other people who look at the source will be able to read it easier than having to spend hours trying to decipher what exactly the algorithm does. A program will usually have many source code files, which can run into even thousands depending on the complexity of the program. For the program to run on a computer, the source code needs to be compiled so that it will be in a language that the computer can understand. If any changes are made to the source code, it will need to be recompiled for those changes to be incorporated in the program.